In general, as amount of information is increased, a magnetic recording medium is demanded which is of mass storage to record a large quantity of information, as well as low-priced, and preferably enables so-called high speed access that can read out a necessary part within a short time. As an example of such a medium, a hard disc and a high-recording density flexible disc are known, and so-called tracking servo technique, in which a magnetic head accurately scans a narrow track width and generates signals with a high S/N ratio, is playing an important role for realizing such mass storage. In one revolution of disc, a servo tracking signal, an address information signal, a regenerative clock signal and the like are recorded in a predetermined space in so-called prefomat.
The magnetic head is allowed to accurately run over the tracks by reading these prefomat signals and correcting its own position. Recently, the prefomat is fabricated by recording discs one by one or tracks thereof one by one using an exclusive servo writer. However, because such a servo writer is very expensive and the fabrication of prefomat is time-consuming, this process occupies a large part of manufacturing cost and it is desired to reduce cost of process.
Meanwhile, it has been proposed to realize the mass storage by a magnetic transfer method, not by recording tracks one by one in prefomat. For example, such a magnetic transfer method is disclosed in Japanese Unexamined Patent Publication Nos. 63-183623, 10-40544, 10-269566 and etc. The magnetic transfer is a process to execute transfer of a magnetic pattern corresponding to information (for example, a servo signal) born in a master carrier by applying magnetic field for transfer in the state that the master carrier and slave medium are in close contact with each other, wherein recording can be executed statically without changing the relative position between the master carrier and the slave medium, whereby it is possible to execute accurate prefomat recording and the time needed for the recording is very short.
In addition, the magnetic transfer is a process for executing transfer of a magnetic pattern corresponding to information (for example, a servo signal) born in a master carrier by applying magnetic field for transfer in the state that the master carrier and slave medium are in close contact with each other. For example, such a magnetic transfer method is disclosed in Japanese Unexamined Patent Publication Nos. 63-183623, 10-40544, 10-269566 and etc.
Furthermore, if the slave medium is a disc-shaped medium such as a hard disc or a high-recording density flexible disc, magnetic field for transfer is applied by a magnetic field applying apparatus located in one side or both sides of slave medium and consisted of an electromagnet(s) or permanent magnet(s) in the state that disc-shaped master carriers are brought into contact with one or both side surfaces of the slave medium.
In order to improve the quality of transfer in said magnetic transfer, it is an important task how to bring the master carrier and slave medium into close contact without any gap. That is, there will be problems in that if there is poor close contact, a non-magnetic transfer region may generated, and if magnetic transfer is not generated, signal omission may be caused in the magnetic information transferred onto the slave medium, thereby deteriorating the quality of signal, and if the recorded signals are the servo signals, a satisfactory tracking function can not be obtained and reliability will be lowered.
In view of the above circumstances, in order to bring the master carrier and slave medium into close contact without any gap and uniformly in magnetic transfer, it has been proposed to enhance the flatness of surface of a holder and maintaining the master carrier and to adsorb the master carrier in reference to the surface to enhance the flatness of the master carrier itself, thereby securing the close contact of master carrier and slave medium (Japanese Patent Application No. 2001-144296).
The present invention was conceived in consideration of the above problems in mind. The object of the present invention is to provide a magnetic transfer apparatus adapted to enhance the quality of transfer signals by increasing the close contact capability of master carrier and slave medium in magnetic transfer by providing a material having elastic property between the master carrier and the holder.
Also, in a conventional magnetic transfer apparatus, a slave medium is forced down against a master carrier by applying compression force by a compressing means in order to increase the close contact capability between the slave medium and master carrier. Such a mechanical contact force applying method is preferred in that a high pressure can be obtained but difficult to uniformly apply a pressure on the contacted surfaces of slave medium and master carrier.
Due to this, a vacuum method in which the internal side of holder that received a master carrier and a slave medium is adsorbed, thereby obtaining a force for close contact is more preferable because the pressure is uniformly applied all over the entire surface of the holder so that the condition of uniform close contact can be realized. However, in the above vacuum method, the maximum pressure difference between the inside and outside of the holder is about 1 atm., and thus it is impossible to obtain a sufficient force for close contact between the master carrier and slave medium, as it is.
Therefore, the inventors have investigated whether a force for close contact can be increased if the mechanical application of pressure by means of a screw is combined with the vacuum method. However, there was a problem in that if the force was mechanically applied as explained in the above, the distribution of pressure became non-uniform, thereby impinging on the quality of transfer signals. In addition, if the vacuum method with chamber structure was used for bringing the master carrier and the slave medium into close contact with each other, it was difficult to enhance the force for close contact depending the construction of holder and local deformation was occurred due to uneven contact. For example, it can be considered that the holder comprises a lower side chamber for fixing a master carrier and an upper side chamber for pressing down the slave medium against the master carrier, wherein a sealing material such as an O-ring is contactedly inserted between the top surface of lower side chamber and the bottom surface of upper side chamber thereby sealing the receiving space. In this construction, when the internal vacuum level was increased, the sealing material was crumpled and thus both of chambers were directly contacted with each other, whereby it was impossible to apply force any more. Due to this, close contact becomes nonuniform and local signal omission was occurred.
The present invention was conceived in consideration the above problem in mind. The object of the present invention is to provide a magnetic transfer apparatus adapted to be able to execute good magnetic transfer by obtaining a sufficient force for close contact only by means of vacuum adsorption of the internal side of holder when the slave medium and master carrier is brought into close contact with each other.
Also, poor close contact of said master carrier and slave medium occurs sometimes because deposited material is present between the master carrier and slave medium, and a gap occurs near the deposited material and causes poor close contact, whereby non-magnetic transfer area may be produced. When magnetic transfer was executed over a number of times, it has been found that signal omission caused by such deposited material is usually produced at the periphery of closely contacted surfaces of master carrier and slave medium. According to the analysis of the deposited material, there were a number of particles formed from components identical to those of the elastic member interposed between the master carrier and the holder for receiving and bring the slave medium and the master carrier into confronted close contact in order to enhance the close contact capability of the master carrier and slave medium.
The present invention was conceived in consideration of the above problem in mind. The object of the present invention is to provide a magnetic transfer apparatus adapted to improve the quality of signal by reducing the generation of signal omission in magnetic transfer.
In addition, the conventional magnetic transfer is executed by bringing a master carrier and a slave medium into close contact with each other, wherein it is required to perform the positioning of master carrier and slave medium in the state of close contact. Because the master carrier and slave medium undergo friction at the time of positioning, as magnetic transfer is repeated, the shape of patterned surface of the master carrier (unevenness shape) that bore information will be abraded and the accuracy of transfer will be degraded. Furthermore, the unevenness pattern is generally coated with a magnetic layer, a lubricant layer or the like on a substrate that retains the unevenness pattern, and as it is repeatedly contacted with and released from a number of slave mediums, the magnetic layer on the patterns and the like may be partially deficient or peeled off from the substrate. If the accuracy of transfer is degraded due to the abrasion, release of magnetic layer and the like, it is required to replace the master carrier. However, because such a master carrier is expensive, it is a very important subject in suppressing costs for manufacturing magnetic recording mediums how many slave mediums using one master carrier can execute transfer on.
The present invention was conceived in consideration of the above situation. The object of the present invention is to provide a magnetic transfer method that can execute magnetic transfer on much more slave mediums using one master carrier and can obtain good transfer signals.
In addition, particularly when magnetic transfer is simultaneously executed on both surfaces of slave medium by bringing each of master carriers into contact with each surface of slave medium and applying magnetic field for transfer to the both surfaces, higher accuracy of close contact is required because each of master carriers must be uniformly in close contact with each surface of slave medium. Although said slave medium and master carriers are received within the holder in confronted close contact with each other, the accuracies of holder and of retaining by the holder as well as the accuracy of the master carriers themselves are required.
As a result of analysis of signal omission in a magnetic pattern magnetically transferred to a slave medium by applying magnetic field for transfer to execute magnetic transfer simultaneously on both surface of the slave medium, after one slave medium and two master carriers on both sides of the slave medium were inserted between a upper holder member and a lower holder member and then brought into confronted close contact with each other by applying a force for close contact, it has been found that the positional relationship between the master carriers of both sides has a large influence on the omission of signals.
The present invention was conceived in consideration of this problem in mind. The object of the present invention is to provide a magnetic transfer apparatus adapted to enhance the quality of transfer signals by increasing the close contact capability between the master carriers and slave medium in simultaneous magnetic transfer on both sides.